In relation to front wheel suspension units of motorcycles, the present invention refers particularly to an improvement of the front wheel suspension unit utilizing an eccentric supporter for the purpose of producing excellent buffer effects against impact inputs not only in the vertical direction but also in the horizontal direction of movement.
In conventional motorcycle front-wheel suspension units, front forks consisting of a suspension spring and a hydraulic damper are commonly employed for connecting the cycle body to the wheel, so that the body can move up and down elastically. Even though conventional suspension means of this type may absorb impact force to produce satisfactory buffer effects in the vertical direction when they work with the wheel, they have little effect against an impact force working in the horizontal direction of movement. Namely, they have a defect in that their buffer effects are not very satisfactory in this respect.
In view of above, the inventor previously presented a novel front wheel suspension unit in Ser. No. 499,886 dated Mar. 11, 1974, of the type where an eccentric supporter was utilized so as to resolve the defect mentioned above. Namely, in the said invention, an eccentric cylindrical type supporter is employed, where the hub of the wheel is fitted, rotating freely on roller bearings, to the outer circumference of an eccentric supporter and a bearing shaft is inserted so that rotation occurs in the horizontal direction, passing through the eccentric position, and roller bearings are incorporated in the same range; both ends of the bearing shaft are supported at the lower part of the front fork so that the wheel may revolve around the axle and also describe a circular motion around the bearing shaft. According to the invention, therefore, the wheel revolves around the eccentric supporter and the cycle body is driven smoothly. In such a case, an impact force working on the wheel in the vertical direction may be absorbed and lessened by the extension and contraction of the front fork, and since the wheel is caused to describe a circular motion around the bearing shaft, the wheel may move back and forth, reacting immediately to an impact force in the horizontal direction of movement as well, thus making it possible to produce buffer effects as the horizontal force is converted to a vertical impact force.
Nevertheless, a suspension unit utilizing such an eccentric cylindrical type supporter is not very satisfactory. For one thing, the roller bearings incorporated between the outer circumference of the eccentric supporter and the inner circumference of the wheel hub become large in diameter to an extent such that the circumferential speed becomes very high during high-speed driving, producing revolution noises and shortening the bearing life. Furthermore, since the rated load of roller bearings is specified according to the inner diameter, such large roller bearings fitted to the outer circumference of the eccentric supporter must have a larger rated load than actually required, and this represents another defect in that the unit does not have advantages with regard to weight and cost of the bearings.